Just saunter down there, grab what you need, pay more than what you expected, walk out of parking lot, past the Citizens Bank, take a right and munch away while you walk down Allston Street. Problem solved. You got good family fare in Allston & Brookline. Also, a number of places in the area have this combination of cooked cheese, tomatoes, and bread. There one place called Inbound on Comm. Ave, another called Uno's that I think Yelp has said that that meal from there is good vegetarian family fare. Be careful though, be specific when you say you want the vegetarian option.

Michael's Deli, which is on the other side of Brookline's Harvard Street, on the other side of Coolidge Corner, also serves excellent sandwiches and is very reasonably priced, although it, too, is kind of dark inside, and a lot smaller than Zaftig's Deli, to boot.

I'm an omnivore, but I really like Root in Allston (actually vegan, but you'd never know it), which has plenty to appeal to kids as well as grownups, like a great veggie burger. (I reviewed it for The Improper Bostonian a few months back: http://www.improper.com/going-out/good-seeds/ ) The nearby Grasshopper is a vegetarian pan-Asian (mainly Chinese and Vietnamese) place, also terrific.

If the kids have adventurous palates, any Korean (like Korea Garden), Thai (like Dok Bua), Indian (like Punjab Palace), or Middle Eastern (like Garlic n Lemons) restaurant will have many excellent vegetarian options: there are dozens of those in Allston.

Shabu-shabu (in reality, Chinese hot pot) is also vegetarian-friendly: you choose a couple kinds of broth, noodles or rice, and a plate of veggies (and/or seafood and chicken, if you're one of those hyphenate-vegetarians), and cook them tableside in the broths: a fun communal meal. Shabu-Zen in Allston is one of my favorites for that. FoMu, owned by the nearby Root folks, does vegan ice cream (haven't tried that one yet).